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The volume transport of the Tsugaru warm current (TWC), defined as the branch current of the western boundary current of the North Pacific subtropical gyre flowing through the Tsugaru Strait, is a critical factor affecting the acidification in the strait as well as the surrounding coastal regions by promoting the enhancement of the vertical mixing of the deep water rich in dissolved inorganic carbon. The in-phase sea-level variation along the coast of mainland Japan with a gap at the Tsugaru Strait permits the discharge of the sea surface water from the Sea of Japan to the Pacific Ocean, which is significantly correlated to the variation in the sea-level difference across the Tsugaru Strait, being possibly related to that in the TWC volume transport. Furthermore, by averaging the wind-driven Sverdrup streamfunction along the eastern coast of mainland Japan—from the southern end of Kyushu (30 ∘ N) to the separation latitude of the Kuroshio (36 ∘ N)—and scaling by a factor of the ratio between the depths of the Tsushima Strait and the East China Sea, we obtained the volume transport varying similarly with the sea-level difference across the Tsugaru Strait. As obtained, the interannual wind stress variation in this latitude band to the east of mainland Japan on the North Pacific is suggested to altered the strength of the TWC. [ABSTRACT FROM AUTHOR]

Linear trends in Kuroshio transport during a recent global warming hiatus (1998–2013) were evaluated using long‐term ferryboat ADCP (acoustic Doppler current profiler) data and tidal gauge data in the Tokara Strait south of Japan. The Kuroshio exhibited a remarkable weakening trend of approximately 0.05 Sv year−1 (1 Sv = 106 m3 s−1). The pycnocline in the weakened Kuroshio was relaxed and displayed shoaling at the offshore edge, which was attributed to vertical thermocline displacement rather than to water mass modification. Importantly, Kuroshio transport trends in the Tokara Strait were affected by sea surface height anomalies, which were driven by the combined effects of the clockwise baroclinic‐mode coastal trapped wave propagation along the southern coast of Japan and downstream Kuroshio advection in the East China Sea. Both features were induced by wind stress curl changes related to the global warming hiatus over the North Pacific. Plain Language Summary: The Kuroshio is the western boundary current in the wind‐driven subtropical circulation of the North Pacific. It exits the East China Sea and flows into the North Pacific through the Tokara Strait between the Yakushima and Amami Oshima Islands to the south of Kyushu, Japan. This study revealed that the Kuroshio transport through the Tokara Strait showed a remarkable weakening trend along with a northward shift during 1998–2013. Changes in the wind stress curl in the high (low)‐latitude band over the North Pacific during the global warming hiatus exhibited negative (positive) tendencies, leading to anomalously high (low) sea surface heights. The high (low) sea surface height anomaly arrived at the onshore (offshore) side of Tokara Strait from the high (low)‐latitude band decreasing Kuroshio transport because of geostrophy. Key Points: Kuroshio transport in the Tokara Strait south of Japan decreased by ∼4% during 1998–2013, indicating a rate of about 0.05 Sv year−1Shoaling of the offshore pycnocline in the Kuroshio was due to vertical thermocline displacement rather than to modified water massDynamic‐topography propagation pathways from the northern and southern interior regions caused weakened Kuroshio transport in the hiatus [ABSTRACT FROM AUTHOR]

Taiwan Strait (TWS) plays a crucial role in material exchange and nutrient budget between the South China Sea and the East China Sea. In this study, we investigate the variability of volume transport in the TWS and its response to tropical Madden–Julian Oscillation (MJO) convection based on the simulated results from a three-dimensional operational numerical model. Validated by the observational data, the model generally reproduced the physical field well. The volume transport in the TWS has strong seasonal cycles as well as higher-frequency variations. Intra-seasonal fluctuations dominate the along-strait currents variability, while secondary and the last signal are seasonal one and inter-annual variability, respectively. Overall, the along-strait wind stress plays a more important role in controlling the variability of volume transport in the TWS than the pressure gradient induced by north-to-south sea level slope. At intra-seasonal time scales, the volume transport in the TWS varies with the movement of the tropical MJO convection from Indian Ocean eastward to the western Pacific Ocean. These oceanic anomalies are related to atmospheric anomalies, with a distinct physical linkage from the tropical atmosphere to the mid-latitude ocean. The tropical MJO deep convection can modify the upper tropospheric heights and generate a wave train pattern that propagates to mid-latitudes. In addition, these anomalous upper tropospheric heights modulate the surface pressure, resulting in a cyclonic anomaly. The upper tropospheric heights anomaly and its corresponding mean sea level pressure anomaly move eastward in the MJO cycle following the migrating MJO heat source in the tropics from phase 2 to 5. Consequently, surface winds change as the cyclonic anomaly moves from central China to the east of Japan, resulting in a northeast volume transport anomaly during MJO phase 2 and 3 and a southwest volume transport anomaly during MJO phase 4 and 5. • Hydrodynamics in Taiwan Strait were reproduced by an operational numerical model. • Wind dominates the volume transport in TWS than the surrounding pressure gradient. • Roles of tropical MJO on volume transport in the TWS are elaborated. [ABSTRACT FROM AUTHOR]

The volume transport of the Kuroshio, the western boundary current of the North Pacific subtropical gyre, varies vigorously due to merging of disturbances propagating from the entire North Pacific. Taking into account the recirculation in the Shikoku Basin by the zonal observation line at 30°N to the west of the Izu-Ogasawara Ridge, we estimated the volume transport in the top 1,000 m layer toward the Kuroshio Extension region. The volume transport of the local recirculation gyre in the Shikoku Basin increases associated with the westward extension of the gyre, particularly in the period of the large meandering path of the Kuroshio south of Japan. Meanwhile, most of the transport variations toward the Kuroshio Extension region correspond to those of the Kuroshio transport on the continental slope south of Japan, which vary independently of those of the recirculation gyre. [ABSTRACT FROM AUTHOR]

Abstract: Direct velocity measurements undertaken using a nine-system mooring array (M1–M9) from 2004 to 2005 and two additional moorings (M7p and M8p) from 2003 to 2004 reveal the spatial and temporal properties of the deep-circulation currents southwest of the Shatsky Rise in the western North Pacific. The western branch of the deep-circulation current flowing northwestward (270–10°T) is detected almost exclusively at M2 (26°15′N), northeast of the Ogasawara Plateau. It has a width less than the 190km distance between M1 (25°42′N) and M3 (26°48′N). The mean current speed near the bottom at M2 is 3.6±1.3cms−1. The eastern branch of the deep-circulation current is located at the southwestern slope of the Shatsky Rise, flowing northwestward mainly at M8 (30°48′N) on the lower part of the slope of the Shatsky Rise with a mean near-bottom speed of 5.3±1.4cms−1. The eastern branch often expands to M7 (30°19′N) at the foot of the rise with a mean near-bottom speed of 2.8±0.7cms−1 and to M9 (31°13′N) on the middle of the slope of the rise with a speed of 2.5±0.7cms−1 (nearly 4000m depth); it infrequently expands furthermore to M6 (29°33′N). The width of the eastern branch is 201±70km on average, exceeding that of the western branch. Temporal variations of the volume transports of the western and eastern branches consist of dominant variations with periods of 3 months and 1 month, varying between almost zero and significant amount; the 3-month-period variations are significantly coherent to each other with a phase lag of about 1 month for the western branch. The almost zero volume transport occurs at intervals of 2–4 months. In the eastern branch, volume transport increases with not only cross-sectional average current velocity but also current width. Because the current meters were too widely spaced to enable accurate estimates of volume transport, mean volume transport is overestimated by a factor of nearly two, yielding values of 4.1±1.2 and 9.8±1.8Sv (1Sv=106 m3 s−1) for the western and eastern branches, respectively. In addition, a northwestward current near the bottom at M4 (27°55′N) shows a marked variation in speed between 0 and 20cms−1 with a period of 45 days. This current may be part of a clockwise eddy around a seamount located immediately east of M4. [Copyright &y& Elsevier]

Abstract: Recent observations of hydrography, currents and volume transports in the straits of the East/Japan Sea are reviewed. It is newly found that bottom cold water in the Korea/Tsushima Strait originating from the northern region of the East/Japan Sea appears not only in summer and autumn but also in winter. Intensive observations in the Korea/Tsushima Strait revealed two distinct cores of northeastward currents in the upper layer of the western and eastern channels. Mean volume transport through the Korea/Tsushima Strait is calculated as 2.5±0.5 Sv from four-year direct and indirect measurements. As continuous monitoring has started in the Tsugaru and Soya Straits, understanding of temporal variability of currents and volume transports through the straits is in progress. For the first time, simultaneous time series of volume transports are available in the Korea/Tsushima and Tsugaru Straits during the winter of 1999–2000. Ouflow through the Tsugaru Strait accounts for about 70% of inflow through the Korea/Tsushima Strait for this period. [Copyright &y& Elsevier]